342 W. J. CROZIER 



of the sea water (down to 80 per cent of the original concentra- 

 tion), whereas the rate of pulsation in intact medusae (p. 28) is 

 not increased in this way ; but in his tables no records are given 

 of the pulsations of entire medusae in sea water of the critical 

 concentrations (95 per cent, 90 per cent). It might appear from 

 the records in my figure 28 that there is some tendency on the 

 part of diluted sea water to preserve in the excised cloacal ends 

 of Stichopus a higher rate of pulsation during the later stages of 

 their history, than is the case with the 'control' pieces in 100 

 per cent sea water. But, as a matter of fact, this is not so, since 

 there was enough variation in these records and in the controls 

 to prohibit a conclusion of this sort. The matter was studied 

 more carefully with 90 per cent and 95 per cent sea water ; no 

 increase in pulsation frequency was discoverable upon diluting 

 to these concentrations sea water in which amputated cloacal 

 ends were pulsating. • 



b) Non-electrolyte solutions. It was found by Loeb ('00 '') 

 that in solutions of non-conductors the isolated center of Gonio- 

 nemus did not exhibit rhythmic contractions. This has in 

 general been the experience of others employing a variety of 

 pulsating mechanisms, namely, that in a medium free from salts 

 but with its osmotic pressure made up to normal by dissolved 

 non-electrolytes, rhythmic contractions are either not initiated 

 or do not continue for any length of time. According to Mayer 

 ('14 '') this physiological inefficiency, of sugars and the like, is 

 also apparent in nerve-conduction in Cassiopea. 



The results of experiments in which the isolated cloacal end 

 of Stichopus was placed in solutions of non-electrolytes may be 

 given very briefly. Pieces immersed in solutions of sucrose, 

 lactose,' maltose, or glycerin theoretically isosmotic with sea 

 water (i.e., 0.9 to 1.0 M) did not pulsate for more than about 15 

 minutes, the actual time for the duration of pulsation varying 

 from 2 to 25 minutes. Irritability to mechanical stimulation 

 disappeared after about half an hour. Such pieces did not 

 recover on return to sea water. In these tests the amputated 

 cloacal end was allowed to begin its pulsation in sea water and 

 to continue there for about 10 minutes; the pieces were then 



